1. Field of the Invention
The present invention relates to spare lines for recovery from disconnection and a common line for the prevention of excess current, both of which are provided in a display device.
2. Description of the Related Art
Active-matrix liquid crystal display devices, for instance, have a plurality of data signal lines and scanning signal lines arranged in a matrix pattern, together with thin-film transistors and pixel electrodes connected to the transistors in the vicinity of intersection points of the data signal lines and the scanning signal lines. Display screen images are displayed by changing the status of orientation of liquid crystal upon feeding signal potential to the pixel electrodes through the data signal lines under on/off control of the thin-film transistors through the scanning signal lines.
Recently, in response to a need for better quality of display images, the width of the data signal lines has become extremely narrow, namely, less than 10 μm, and in actual instance, 6 μm. As a result, breaks tend to occur in a manufacturing process. For instance, dust getting in during film formation and only a pinhole appearing on a resist mask during etching result in breaks. Such breaks in the data signal lines cause black lines in normally black mode or bright lines in normally white mode on a screen because proper signal potential cannot be fed to the pixel electrodes located behind the breaks. Thus, a critical defect in the quality of display images arises.
As a solution for recovery from such disconnection, the following method has been suggested. That is to say, spare lines are provided so as to extend from the vicinity of the signal input-side ends of data signal lines toward the vicinity of the opposite ends (i.e., below a display area), passing through an external substrate of a panel. The end of a line part behind a break in the data signal line is connected to the spare line by laser melting, so that signals can be supplied to the line part behind the break. According to the method above, the spare lines are formed in advance in a pattern as illustrated in FIG. 7 below the display area (i.e. in a lower area of the panel), so that the broken data signal line is connected to one of the spare lines for recovery from defects.
With regard especially to large-size display devices such as televisions and monitors, a spare line is wide, and a line part behind a connection point (an unnecessary line part) is long. This increases a load on the unnecessary line part. Therefore, as illustrated in FIG. 8, the unnecessary line parts (shaded portions in the figure) have to be removed.
However, a wide spare line is not easy to cut by laser cutting, for instance. This gives rise to the problem that cutting is laborious or proper cutting is impossible.